Known techniques to secure migration transparency of a UE (User Equipment) in an IP network include GTP (GPRS Tunneling Protocol) on a 3GPP (Third Generation Partnership Project) access network and DSMIP (Dual Stack Mobile IP) on a Non-3GPP access network. As such techniques, PMIP (Proxy Mobile IP) also is known, which can be used on the access networks supporting 3GPP as well as on the access networks supporting Non-3GPP (refer to the following Non-Patent Document 1 and Non-Patent Document 2).
FIG. 1 shows an exemplary configuration of a communication network using PMIP. FIG. 1 shows the configuration including a UE 1 (User Equipment, which may be called a mobile node (MN) also), a MME 7 (Mobility Management Entity) to perform mobility management of the UE 1, a base station (eNB (eNode B) not shown) to transmit data to the UE 1 by radio waves, a SGW 6 (Serving Gateway, which may be called a MAG (Mobility Anchor Gateway) or the like in PMIP) to perform user data path control between base stations, a PGW 5 (Packet Gateway, which may be called a home agent (HA) in DSMIP, a local mobility anchor (LMA) in PMIP or the like) to assign an address to the UE 1 and to perform user data path control with the SGW 6, an ePDG 8 (evolved Packet Data Gateway) having a function to establish a PDN connection in a Non-3GPP access network 3 and functioning to protect a packet with the UE 1 during transmission/reception to/from the UE 1 and a DNS (Domain Name System) server 9 to hold a set of a URI (Universal Resource Identifier) and an IP address of the ePDG 8. Although FIG. 1 does not explicitly show the connection form of the DNS server 9, the DNS server 9 is accessible from a core network 4 and each access network (a 3GPP access network 2 and the Non-3GPP access network 3).
In FIG. 1, when the UE 1 performs a communication with a foreign network via the 3GPP access network 2 and the core network 4, a PDN connection has to be established between the UE and the PGW. The UE 1 acquires an IPv4 address (this may be called an IPv4 home address, an IPv4 HoA or the like) assigned by the PGW or an IPv6 prefix (this may be called an IPv6 home prefix or the like) during the establishment of the PDN connection to establish an EPS bearer (Evolved Packet System Bearer) communicable with the foreign network. When PMIP is applied for the establishing procedure of the PDN connection, the SGW 6 uses a proxy binding update (hereinafter called PBU) message to inform the PGW 5 of local information (e.g., the address of the SGW) on the location of the UE 1. Thereby, the PGW 5 creates a binding cache entry (hereinafter called BCE) that is the association of the reported information on the location of the UE 1 (hereinafter called positional information) with the already allocated IPv4 home address, IPv6 home prefix or the like and holds the BCE in a binding cache (hereinafter called a BC).
When an IPv6 prefix is allocated from the PGW 5, the UE 1 creates, from the allocated IPv6 prefix, an IPv6 address with the procedure specified by IETF (Internet Engineering Task Force), i.e., IP address automatic creation procedure or the like. This IPv6 address is called an IPv6 home address, an IPv6 HoA or the like. The PGW 5 refers to the BCE to check the destination address of the received packet addressed to the UE 1 (i.e., the IPv4 home address or the IPv6 home address) against an IP address registered in the BCE. When a result of the checking shows a corresponding BCE, the PGW 5 fetches positional information of the UE 1 corresponding to the IP address registered in the BCE and transfers a packet to the UE 1 via the SGW 6. That is to say, even when a network to be connected is changed, the SGW 6 informs the PGW 5 of network information on the current location of the UE 1 or the like and the PGW 5 registers (updates) a BCE, whereby the UE 1 can receive a message addressed to the HoA of the UE 1 correctly even after a handover of networks. In general, the SGW 6 transmits a PBU message regularly in accordance with an operator policy for network management or at the time of a handover followed by the movement of the UE 1.
Further, the UE 1 can have HoAs of different IP versions at the same time (e.g., IPv6 HoA (or IPv6 prefix) and IPv4 HoA) and the UE 1 can transmit/receive a packet using each HoA. For instance, when the UE 1 already acquires the IPv4 HoA and the IPv6 HoA and is in a state of capable of transmitting/receiving a packet with the PGW 5 using each HoA, the UE 1 has a PDN connection of an IPv4v6 PDN type (PDN type) with the PGW 5. Alternatively, the UE 1 can have a PDN connection of IPv4 PDN type and a PDN connection of IPv6 PDN type, and can transmit/receive a packet using each HoA. Information on such PDN connections of the UE 1 is stored in EPS bearer context that the MME 7 or the SGW 6 has or P-GW context that the PGW 5 has. A packet is transmitted/received between the UE 1 and each device on the basis of these contexts.
Further, when the UE 1 having a PDN connection of IPv4v6 PDN Type and in a state of transmitting/receiving a packet performs a handover to a network supporting a PDN connection of IPv4v6 PDN type, such EPS bearer context or P-GW context is used. Thereby, even after the handover, the UE 1 maintains the PDN connection of IPv4v6 PDN Type and can transmit/receive a packet using bearer corresponding to the IPv4 HoA and the IPv6 HoA.